Laurent Bercot:
The real question is, why is there a "umask" binary that's not the one
from execline? Non-chainloading non-builtin umask is nonsense, just
like non-chainloading non-builtin cd.
Not quite. People find uses for these things, and as the SUS rationale
points out, for every potentially useless external equivalent of a
(non-special) built-in command someone has come up with an arcane actual
use for it. Even "cd".
*
https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xcu_chap01.html#tag_23_01_07
* https://unix.stackexchange.com/q/50058/5132
The POSIX model is therefore that all non-special built-ins are also
available as executables; or, rather, that all of the standard utilities
that are not special built-ins are simply *available* (via execvp(),
find -exec, env, and *all of the other* ways that standard utilities can
be invoked), and whether they are built-in or not, to a shell or
otherwise, is an implementation detail as far as actually invoking the
utility is concerned. (Very few shells truly conform to this, but the
Watanabe shell largely does in its non-native mode.)
* https://unix.stackexchange.com/q/347188/5132
* https://unix.stackexchange.com/q/496259/5132
nosh, not being a shell, is not bound by this. Its built-ins are found
before a PATH search is enacted. So it actually does what M. Geraghty
mistakenly thought execline was doing. It finds its own built-ins in
preference to finding external commands; so invoking "umask" (without
directory name prefix) within a nosh script will always invoke the
built-in chain-loading one, irrespective of PATH. (Several of the
non-conformant shells do this, too, giving their built-ins unequivocal
precedence over a PATH search. Some even document this behaviour. But
it is not standard-conformant for a shell.)
* https://unix.stackexchange.com/a/496377/5132
* http://jdebp.uk./Softwares/nosh/guide/commands/exec.xml
execline always searches PATH. It does not have built-ins like nosh or
shells, in the first place. There's a quirk about when changes to PATH
take effect, and it does not quite have the POSIX semantics for when
PATH is not set, but other than that it actually has the POSIX model
behaviour: Commands are located using PATH, and what command one invokes
by the name "umask" is entirely determined by what PATH lists.
* https://unix.stackexchange.com/a/448799/5132
